The effect of congenital heart disease on early social relationships was assessed by observing 42 infants with the disease and 46 healthy infants in a standardized laboratory setting with their mothers. Significantly fewer infants with congenital heart disease, in comparison with healthy peers, were considered to have secure relationships with their mothers. The quality of the infant-mother relationship in the group with congenital heart disease was not related to parents' reports of their own stress or psychologic well-being. Severity of illness did not have a direct effect on the quality of the infant-mother relationship, but securely attached infants showed more subsequent improvement in health than insecurely attached peers showed. Attention to the infant-mother relationship in clinical care may improve the social development of babies with congenital heart disease and may have positive effects on physical health as well.